Heinemann and Glenn1 observed that certain bacteria were agglutinated in milk serum and concluded that this was possibly related to the germicidal action of milk. Chambers2 made similar observations but could find no correlation between agglutination and germicidal action. Hobbs3 examined a variety of milk organisms and attributed the clumping effect of milk on some of them to agglutinins which were probably non-specific. More recently, Wright and Tramer4 demonstrated that certain organisms noted for slow acid production in activity tests of cheese starters were agglutinated in heat-treated milk. The lag in acid production was shown to be due not to agglutination but to the removal of the agglutinated organisms by the rising cream.